Method and apparatus to control discharge cooling in a refrigeration system

ABSTRACT

A method and apparatus for operating a discharge cooling cycle in a refrigeration system. The method includes determining a first operating condition of the refrigeration system. The method also includes, based on the determination of the operating condition, activating an evaporator fan for a first predetermined period of time, deactivating the evaporator fan for a second predetermined period of time, and repeating the activating and deactivating until a second operating condition is detected.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application claims priority to commonly assigned U.S.Provisional Patent Application No. 61/343,472, filed Apr. 29, 2010,entitled “DISCHARGE COOLING”, which is hereby incorporated by referenceinto the present application as if fully set forth herein.

TECHNICAL FIELD

This disclosure is generally directed to refrigerated vending machinesand more particularly to an apparatus and method to control a dischargegas temperature to prevent premature compressor failure.

BACKGROUND

During operation of a refrigeration system of a refrigerated vendingmachine, changes in the environment inside or outside of the vendingmachine may cause the compressor in the system to become too hot. Whenthe compressor overheats, the compressor may burn out, crack a valvehead, or otherwise be damaged. Even if the compressor is not damaged, anoverheated compressor impedes the heat: transfer by the cooling systemfrom products contained within the vending machine. This reduced heattransfer may increase operating costs, decrease efficiency, and reduceproduct cooling.

SUMMARY

According to one embodiment of the present disclosure, a method ofoperating a refrigeration system includes determining a first operatingcondition of the refrigeration system. The method also includes, basedon the determination of the first operating condition, activating anevaporator fan for a first predetermined period of time, deactivatingthe evaporator fan for a second predetermined period of time, andrepeating the activating and deactivating until a second operatingcondition is detected.

In another embodiment, an apparatus includes a refrigeration system thatincludes a compressor and an evaporator fan. The apparatus also includesa controller communicatively coupled to the refrigeration system. Thecontroller is configured to determine a first operating condition of therefrigeration system. The controller is also configured, based on thedetermination of the first operating condition, to activate theevaporator fan for a first predetermined period of time, deactivate theevaporator fan for a second predetermined period of time, and repeat theactivation and deactivation until a second operating condition isdetected.

In still another embodiment, a vending machine includes a productstorage area and a refrigeration system that includes a compressor andan evaporator fan, the refrigeration system configured to cool theproduct storage area. The vending machine also includes a controllercommunicatively coupled to the refrigeration system. The controller isconfigured to determine a first operating condition of the refrigerationsystem. Based on the determination of the first operating condition, thecontroller is also configured to activate the evaporator fan for a firstpredetermined period of time, deactivate the evaporator fan for a secondpredetermined period of time, and repeat the activation and deactivationuntil a second operating condition is detected.

Other technical features may be readily apparent to one skilled in theart from the following figures, descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure and its features,reference is now made to the following description, taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates a block diagram of a vending machine according to anembodiment of the disclosure;

FIG. 2 is a state diagram of refrigeration control of a vending machineaccording to an embodiment of the disclosure; and

FIG. 3 depicts a method of using a discharge cooling cycle according toan embodiment of the disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 3, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged vending machine.

The present disclosure provides a method and apparatus to controloperation of an evaporator fan in a refrigeration system of an appliancesuch as a vending machine. The method and apparatus according to thisdisclosure offers many advantages. For example, the apparatus allows forgreater flexibility, reliability, and efficiency of the refrigerationsystem. Also, the apparatus protects the compressor by maintaining thecompressor at a stable temperature. Moreover, the apparatus may be usedto enhance the energy efficiency of the evaporator.

In many refrigeration systems, the evaporator is the source of thechilled air used to cool the interior of the system. Often, theevaporator resembles a radiator in physical appearance. The evaporatoruses a liquid refrigerant to lower the temperature of the chilled air asdescribed herein.

When the liquid refrigerant leaves a small capillary tube, therefrigerant is injected into one or more larger tubes of the evaporator,thus causing a pressure drop. This pressure drop allows the refrigerantto expand into a gaseous state. This change of state from liquid to gasabsorbs heat, thus lowering the temperature of the refrigerant. Thecooled, gaseous refrigerant travels through the evaporator tubes. Aircirculates across the cooled evaporator tubes, thus lowering thetemperature of the air. The refrigerant then passes out of theevaporator and to the compressor to begin the circulation process again.

One problem encountered in refrigeration systems is how to maintain thecompressor at a suitable operating temperature. Chilled suction gasreturning to the compressor from the evaporator helps to cool thecompressor. However, too much air exchange at the evaporator may raisethe temperature of the suction gas, thus reducing its cooling ability.This can cause the compressor to overheat.

Disclosed are methods and apparatus used to cycle the evaporator fan inorder to control the temperature of the suction gas returning to thecompressor. By controlling the temperature of the suction gas, thesystem keeps the compressor temperature stable, thus protecting thecompressor from excessive wear or damage.

Prior methods of protecting the compressor rely on excessive amounts ofcondensing capacity that is only used under extreme conditions. Inaccordance with the disclosed methods and apparatus, regardless of thecondition, the compressor is protected during abusive periods ofoperation, e.g. when the condenser gets dirty, if a large quantity ofhot products are loaded in the vending machine, or if the ambienttemperature outside the vending machine exceeds normal limits.

FIG. 1 illustrates a block diagram of a vending machine according to anembodiment of the disclosure. The vending machine 100 includes a vendingmachine controller (VMC) 102 that operates to control functions of thevending machine 100. Such functions include vending, payment, andrefrigeration functions.

The vending machine 100 includes a temperature probe 104 that iscommunicatively coupled to the VMC 102. The temperature probe 104 islocated in a position within the vending machine 100 that enables thetemperature probe 104 to sense a temperature that is representative ofeither the temperature of products stored in the vending machine 100,the temperature of the air inside the cooled portion of the vendingmachine 100, or both. For example, such a location may be in a productcompartment of the vending machine 100 in which products are stored, orin a return air duct for air returning from the compartment to bechilled.

The vending machine 100 also includes a refrigeration system 106 thatcontrols the temperature of the product compartment of the vendingmachine 100, in which products are stored. In the refrigeration system106, a refrigerant is compressed in a compressor 108. The compressedrefrigerant is cooled in condenser coils and then passes through anexpansion device. The low pressure refrigerant flows through evaporatorcoils before returning to the compressor. An evaporator fan 110 pullsair from the product compartment over the evaporator coils and pusheschilled air back into the product compartment. The compressor 108 andthe evaporator fan 110 are communicatively coupled to the VMC 102, whichcontrols their operation. In some embodiments, the temperature probe 104is located in a position that that enables the temperature probe 104 tosense a temperature of the evaporator coils.

Typically, the product compartment of the vending machine 100 isaccessible via a door for restocking products. The vending machine 100further includes a door sensor 112 communicatively coupled to the VMC102. The door sensor 112 provides an indication of whether the door isopen or closed.

Although FIG. 1 depicts one example of a vending machine 100, variouschanges may be made to FIG. 1. For example, in some embodiments, thecontrol functions of the VMC 102 may be implemented in a singlemicrocontroller or microprocessor. In other embodiments, the controlfunctions of the VMC 102 may be distributed across a plurality ofmicrocontrollers or microprocessors.

FIG. 2 illustrates a state diagram 200 of refrigeration control by avending machine controller (e.g., the VMC 102) of a vending machineaccording to an embodiment of the disclosure. Often, the door thatprovides restocking access to the product compartment of the vendingmachine 100 comprises an entire sidewall or front of the compartment. Asa result, a significant quantity of chilled outside air can enter thecompartment when the door is opened.

The introduction of outside air and unchilled products to the productcompartment during restocking may cause the temperature within thecompartment to rise. Similarly, when power is turned off to the vendingmachine 100, the refrigeration system 106 stops functioning and thetemperature within the product compartment increases. This state isillustrated in FIG. 2 as a Door Open/Power Off state 202. From any stateof the state diagram 200, when the door is opened, the VMC 102 entersthe Door Open/Power Off state 202. Similarly, when power to the vendingmachine is interrupted, the VMC 102 enters the Door Open/Power Off state202.

When the door is closed or the power is turned back on, the vendingmachine 100 enters one of two modes during which the VMC 102 operatesthe refrigeration system 106 to quickly bring the temperature within theproduct compartment to a desired operating temperature.

When the door sensor 112 indicates that the door is closed, the VMC 102moves from state 202 to either a Reload state 204 or a Pulldown state206, according to an initial temperature in the product compartment, assensed by the temperature probe 104. In the exemplary embodiment, if theinitial temperature is less than 73 degrees Fahrenheit, the state of VMC102 changes to the Reload state 204. If the initial temperature isgreater than or equal to 73 degrees Fahrenheit, the state of VMC 102changes to the Pulldown state 206.

In both the Reload state 204 and the Pulldown state 206, the VMC 102controls the refrigeration system 106, including controlling thecompressor 108 and the evaporator fan 110, which are explained in moredetail below. In either the Reload state 204 or the Pulldown state 206,if the VMC 102 determines that the temperature probe 104 has reached apredetermined temperature set point, the state of the VMC 102 changes toa Steady State Temperature state 208. During the Steady StateTemperature state 208, the VMC 102 controls the refrigeration system106, including the compressor 108 and the evaporator fan 110.

In some embodiments, the predetermined temperature set point is 35degrees Fahrenheit. In other embodiments, the predetermined temperatureset point is 37 degrees Fahrenheit. While particular predeterminedtemperature set points have been described, it will be understood thatin still other embodiments, other predetermined temperature set pointsmay be utilized. In yet other embodiments, the predetermined temperatureset point is set by an operator of the vending machine 100.

Although FIG. 2 depicts one example of a state diagram of refrigerationcontrol of a vending machine, various changes may be made to the controlflow. For example, in some embodiments, the state diagram 200 mayinclude more or fewer states. In some embodiments, the various statesmay be arranged in a different order or triggered by other temperaturepoints.

In both the Reload state 204 and the Pulldown state 206, the compressor108 may operate continuously or may operate with duty cycles havingbrief “off” periods. When the compressor 108 operates continuously orwith few breaks, the compressor 108 may have a tendency to overheat. Toavoid or mitigate overheating at the compressor 108, the condensingtemperature of the vapor coming out of the compressor 108 (also referredto as the discharge gas temperature) is preferably monitored with one ormore sensors. When the condensing temperature (discharge gastemperature) is sensed to be rising and reaching an unacceptable level,this can indicate that the compressor 108 is overheated or is in dangerof overheating.

In accordance with embodiments of the present disclosure, a dischargecooling cycle is used to maintain the compressor 108 at a suitableoperating temperature. The discharge cooling cycle reduces the time thatthe evaporator fan 110 operates. In many refrigeration systems, theevaporator fan operates roughly in coordination with the compressor.Thus, whenever the compressor operates, the evaporator fan normally alsooperates. However, in the discharge cooling cycle disclosed herein, theevaporator fan 110 can be deactivated during periods when the compressor108 is operating. Shutting off the evaporator fan 110 allows thecompressor 108 to cool down and keep the discharge gas temperaturewithin approved guidelines. By stopping the evaporator fan 110, theevaporator runs at a colder temperature and the return gas to thecompressor 108 should be at a lower temperature, in turn cooling thecompressor 108 and reducing the discharge gas temperature.

In one embodiment of the discharge cooling cycle, the evaporator fan 110is operated using a duty cycle of approximately thirty (30) minutes “on”and approximately five (5) minutes “off”. In another embodiment, theevaporator fan 110 is operated using a duty cycle of approximatelytwenty (20) minutes “on” and approximately four (4) minutes “off”. Otherduty cycles having other periods of “on” and “off” are possible, and canbe determined and programmed in advance, or can be determineddynamically at run time. In still another embodiment, the evaporator an110 is run on a variable basis, keying off the discharge gas temperatureor a liquid line temperature. The time that the evaporator fan 110 isrun may be based upon the design of the evaporator that is implementedin the refrigeration system 106. One or more sensors (e.g., temperatureprobe 104) may be used to determine the optimum time or duty cycle foroperating the evaporator fan 110.

The discharge cooling cycle may be executed whenever the compressor 108operates for an extended period of time. Thus, the discharge coolingcycle may be executed during the Reload state 204 or the Pulldown state206. During the Reload state 204 or the Pulldown state 206, thecompressor 108 operates continuously or almost continuously in order toquickly reduce the temperature inside the vending machine 100.

In some embodiments, the discharge cooling cycle is executed during theSteady State Temperature state 208. Usually, during the Steady StateTemperature state 208, the temperature inside the vending machine 100 isat or near the desired operating temperature. Thus, the compressor 108operates using shorter cycles to maintain the desired operatingtemperature. However, during periods of higher ambient temperatures(e.g., in a warehouse setting, where the ambient temperature outside thevending machine can rise above 100 degrees Fahrenheit), the compressor108 may run for extended periods simply to maintain the vending machine100 at the desired operating temperature. Thus, during such Steady StateTemperature states 208, the discharge cooling cycle is useful in coolingthe compressor 108.

In other embodiments, the discharge cooling cycle is executed in a dustyor dirty environment where the condenser 108 can get dirty quickly. Dirtbuildup on or around the condenser 108 can reduce ventilation and causethe condenser 108 to overheat more quickly.

FIG. 3 depicts a method of using a discharge cooling cycle according toan embodiment of the disclosure. The method shown in FIG. 3 is forillustration only. Other embodiments of the method could be used withoutdeparting from the scope of this disclosure.

First, the VMC 102 determines the occurrence of a first operatingcondition in the refrigeration system 106 or the vending machine 100(block 310). In one embodiment, the first operating condition is thestart of a Reload state 204 or a Pulldown state 206. In anotherembodiment, the first operating condition is a discharge gas temperatureabove a certain temperature. In yet another embodiment, the firstoperating condition is an ambient air temperature outside the vendingmachine 100 above a certain temperature.

Next, based on the occurrence of the first operating condition, theevaporator fan 110 is activated for an “on” period of a duty cycle(block 320). In an embodiment, the evaporator fan 110 is activated forapproximately thirty (30) minutes. In another embodiment, the evaporatorfan 110 is activated for a longer or shorter period of time. Next, afterthe “on” period, the evaporator fan 110 is deactivated for an “off”period of a duty cycle (block 330). The evaporator fan 110 may bedeactivated for approximately five (5) minutes, or a longer or shorterperiod of time.

Next, the discharge cooling cycle of the evaporator fan 110 is repeateduntil a second operating condition in the refrigeration system 106 orthe vending machine 100 occurs (block 340). In an embodiment, the secondoperating condition is the end of a Reload state 204 or a Pulldown state206. In another embodiment, the second operating condition is adischarge gas temperature at or below a certain temperature. In yetanother embodiment, the second operating condition is an ambient airtemperature outside the vending machine 100 at or below a certaintemperature.

Upon the conclusion of the discharge cooling cycle, the evaporator fan110 operates according to its standard operating practices. The standardoperating practices are in coordination with the rest of therefrigeration system 106, including the compressor 108.

Although FIG. 3 illustrates one example of a method of using a dischargecooling cycle, various changes may be made to FIG. 3. For example, whileshown as a series of steps, various steps in FIG. 3 may overlap, occurin parallel, occur in a different order, or occur multiple times.

Although the figures above illustrate specific systems, structures, andmethods, various changes may be made to the figures. For example,various components in the systems and structures can be combined,omitted, further subdivided, or moved according to particular needs. Insome embodiments, various functions described above are implemented orsupported by a computer program that is formed from computer readableprogram code and that is embodied in a computer readable medium. Thephrase “computer readable program code” includes any type of computercode, including source code, object code, and executable code. Thephrase “computer readable medium” includes any type of medium capable ofbeing accessed by a computer, such as read only memory (ROM), randomaccess memory (RAM), a hard disk drive, a compact disc (CD), a digitalvideo disc (DVD), or any other type of memory.

It may be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation. The term “or” is inclusive, meaning and/or. The phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like.

While this disclosure has described certain embodiments and generallyassociated methods, alterations and permutations of these embodimentsand methods will be apparent to those skilled in the art. Accordingly,the above description of example embodiments does not define orconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

1. A method of operating a refrigeration system, the method comprising:determining a first operating condition of the refrigeration system; andbased on the determination of the first operating condition, activatingan evaporator fan for a first predetermined period of time, deactivatingthe evaporator fan for a second predetermined period of time, andrepeating the activating and deactivating until a second operatingcondition is detected.
 2. The method of claim 1, wherein the firstoperating condition is a start of a pulldown state or a reload state,and the second operating condition is an end of the pulldown state orthe reload state.
 3. The method of claim 1, wherein the first operatingcondition is a discharge gas temperature above a first predeterminedlevel.
 4. The method of claim 3, wherein the second operating conditionis the discharge gas temperature below a second predetermined level. 5.The method of claim 1, wherein the first operating condition is anambient temperature outside the refrigeration system above apredetermined level and the second operating condition is the ambienttemperature outside the refrigeration system at or below thepredetermined level.
 6. The method of claim 1, wherein the firstpredetermined period of time is approximately thirty minutes and thesecond predetermined period of time is approximately five minutes. 7.The method of claim 1, wherein the refrigeration system is disposed in avending machine.
 8. An apparatus, comprising: a refrigeration systemcomprising a compressor and an evaporator fan; and a controllercommunicatively coupled to the refrigeration system, the controllerconfigured to: determine a first operating condition of therefrigeration system; and based on the determination of the firstoperating condition, activate the evaporator fan for a firstpredetermined period of time, deactivate the evaporator fan for a secondpredetermined period of time, and repeat the activation and deactivationuntil a second operating condition is detected.
 9. The apparatus ofclaim 8, wherein the first operating condition is a start of a pulldownstate or a reload state, and the second operating condition is an end ofthe pulldown state or the reload state.
 10. The apparatus of claim 8,wherein the first operating condition is a discharge gas temperatureabove a first predetermined level.
 11. The apparatus of claim 10,wherein the second operating condition is the discharge gas temperaturebelow a second predetermined level.
 12. The apparatus of claim 8,wherein the first operating condition is an ambient temperature outsidethe refrigeration system above a predetermined level and the secondoperating condition is the ambient temperature outside the refrigerationsystem at or below the predetermined level.
 13. The apparatus of claim8, wherein the first predetermined period of time is approximatelythirty minutes and the second predetermined period of time isapproximately five minutes.
 14. The apparatus of claim 8, wherein theapparatus is disposed in a vending machine.
 15. A vending machine,comprising: a product storage area; a refrigeration system comprising acompressor and an evaporator fan, the refrigeration system configured tocool the product storage area; and a controller communicatively coupledto the refrigeration system, the controller configured to: determine afirst operating condition of the refrigeration system; and based on thedetermination of the first operating condition, activate the evaporatorfan for a first predetermined period of time, deactivate the evaporatorfan for a second predetermined period of time, and repeat the activationand deactivation until a second operating condition is detected.
 16. Theapparatus of claim 15, wherein the first operating condition is a startof a pulldown state or a reload state, and the second operatingcondition is an end of the pulldown state or the reload state.
 17. Theapparatus of claim 15, wherein the first operating condition is adischarge gas temperature above a first predetermined level.
 18. Theapparatus of claim 17, wherein the second operating condition is thedischarge gas temperature below a second predetermined level.
 19. Theapparatus of claim 15, wherein the first operating condition is anambient temperature outside the product storage area above apredetermined level and the second operating condition is the ambienttemperature outside the product storage area at or below thepredetermined level.
 20. The apparatus of claim 15, wherein the firstpredetermined period of time is approximately thirty minutes and thesecond predetermined period of time is approximately five minutes.